A blood cell analyzer is an instrument that detect cells in the blood. It counts and sorts cells, such as leucocytes (white blood cells or WBC), red blood cells, blood platelets, nucleated red blood cells, and reticulocytes.
The most common method used by a blood cell analyzer to detect leucocytes is a laser scattering method, in which by irradiating cell particles flowing through a detection region with light, optical signals reflected or scattered by various categories of particles are collected, and then the optical signals are processed and analyzed so as to sort and count the leucocytes. The collected optical signals may include three types of optical signals, including forward-scattered light, side-scattered light, and fluorescence signals. The forward-scattered light can reflect size information of the cell, the side-scattered light can reflect complexity of an internal structure of the cell, and the fluorescence signal reflects components in the cell that can be dyed by a fluorescent dye, such as DNA and RNA. By means of these optical signals, the leucocytes can be sorted, and the leucocyte count can be obtained at the same time.
According to different pretreatments of blood samples (e.g., reagents being different), detection processes are divided into different detection channels, such as a differential (DIFF) channel, a basophil (BASO) channel and a nucleated red blood cell (NRBC) channel. The BASO channel is used to sort and count leucocytes, while a blood sample is treated with a chemical reagent, the total number of leucocytes is counted by means of side-scattered light and forward-scattered light, and a count of basophil granulocytes in the leucocytes is also provided. The NRBC channel can be used to sort nucleated red blood cells after a blood sample is treated with a fluorescent reagent added therein. The NRBC channel can provide a leucocyte count and a nucleated red blood cell count.
During blood cell detection by a blood cell analyzer, two types of particles cannot be clearly distinguished from each other in some cases, thus affecting particle sorting results. For example, when counting leucocytes, the leucocytes may not be counted accurately due to the influence of interfering particles. The interfering particles may include lipid granules or aggregated PLT (blood platelet) particles. PLT is a part of a blood ghost which is a cell debris structure formed after a sample pretreatment of a blood sample, in which cells such as red blood cells or platelets are subjected to a hypotonic treatment or treated with a reagent, resulting in cell membrane rupture. Generally, the particle size is small, and the forward-scattered light signal is weak. However, in some samples, PLT aggregation may occur and interfering with the leucocyte detection. These interfering particles may overlap with the leucocyte in the scatter diagram. FIG. 1 shows a detection result of the NRBC channel, where an aggregated platelet cluster A1 overlaps with a leucocyte cluster B1 in the forward-scattered light and fluorescence signals. FIG. 2 shows a detection result of the BASO channel, where leucocytes are sorted into a basophil granulocyte cluster A2 and a cluster B2 of other leucocyte particles including lymphocytes, monocytes, neutrophil granulocytes and eosinophil granulocytes. Due to the existence of lipid particles, a lipid granule cluster C2 overlaps with the cluster B2 of other leucocyte particles in a region D2 at a lower end of the forward-scattered light and side-scattered light signals, which may interfere with counting of leucocytes. It can be seen that the existence of these interfering particles in the blood sample will affect the accuracy of the detection results.